Field of the Invention
The present invention is related to the field of organic or molecular materials and their use in connection with electricity, more specifically in electronic, electro-optic, optoelectronic and photovoltaic implementations.
Description of the Related Art
Organic electronics has been widely developed over the past decades because of its potential to simplify and reduce the cost of fabrication of electronic components such as displays, transistors, photovoltaics, medical devices and sensors (see for example: “Materials and applications for large area electronics: solution-based approaches”, Arias et al., Chem. Rev. 2010, 110, 3-24-hereinafter “ref. 1”/“Charge transport physics of conjugated polymer field-effect transistors”, H. Sirringhaus et al., Adv. Mater. 2010, 22, 3893-3898—hereinafter “ref. 2”).
Organic electronics include the use of both molecular materials and polymers which can provide mechanical flexibility and be easily processed on a large scale, also leading to quite inexpensive consumer devices.
One of the most challenging problems for organic electronics is the low charge carrier mobility in organic materials, as well as the disorder in these materials, which hamper its more wide-spread use for devices (see for instance ref. 1: p 7, col 2, 1st paragraph and 3rd paragraph; p 12, column 1, 3rd paragraph; p 13, col 1, 1st paragraph). Much effort over the past decades has therefore been focused on optimizing the organisation of the material or the devices to improve carrier mobility between molecules or molecular units. Nevertheless, mobilities are in the most optimized configurations reported in the literature (refs. 1, 2) in the order of 0.1 cm2/Vs but often a couple of orders of magnitude lower.
This compares very unfavourably with inorganic semiconductors such as Si which is on the order of 103 cm2/Vs due to regular periodic structure of such materials and the associated well defined electronic bands. The low carrier mobility in organic materials stems from the fact that the carriers hop from one molecule or moiety to another in the material.
Therefore, there is a strong demand for significantly improving this feature and to overcome this main drawback of organic and molecular materials, in order to be able to fully exploit the potential use of such materials in the concerned technological fields and technical applications.
On the other hand, it is known that light and matter can enter into the strong coupling regime by exchanging photons faster than any competing dissipation processes. This can be achieved by placing the material in a confined electromagnetic environment, such as a Fabry-Perot (FP) cavity composed of two parallel mirrors that is resonant with an electronic transition in the material. Strong coupling leads to the formation of two polaritonic states, P+ and P−, separated by the so-called Rabi splitting. According to quantum electrodynamics, in the absence of dissipation, the Rabi splitting is given by:
                              ℏΩ          R                =                  2          ⁢                                                                      ℏ                  ⁢                                                                          ⁢                  ω                                                  2                  ⁢                                      ɛ                    0                                    ⁢                  v                                                      ·            d            ·                                                            n                  ph                                +                1                                                                        (        1        )            where ℏω is the cavity resonance or transition energy, ∈0 the vacuum permittivity, v the mode volume, d the transition dipole moment of the material and nph the number of photons present in the system. The last term implies that even in the dark, the Rabi splitting ℏΩR has a finite value which is due to the interaction with the vacuum electromagnetic field. This vacuum Rabi splitting can be further increased by coupling a large number N of oscillators to the electromagnetic mode since ℏΩRN∝√{square root over (N)}. Vacuum Rabi splittings as large as 1 eV have been reported for strongly coupled molecules, thereby significantly modifying the electronic structure of the molecular material as can be seen in the work function, the chemical reactivity and the ground state energy shift (see in particular: Haroche, S. “Cavity quantum electrodynamics” in: J. Dalibard, J. M. Raimond, J. Zinn-Justin (Eds.), Fundamental Systems in Quantum Optics, Les Houches Summer School, Session LIII, North Holland, Amsterdam. 1992/Schwartz, T., Hutchison, J. A., Genet, C. & Ebbesen, T. W. “Reversible switching of ultra-strong coupling” Phys. Rev Lett. 106, 196405 (2011)/Kéna-Cohen, S., Maier, S. A. & Bradley, D. D. C. “Ultrastrongly coupled exciton-polaritons in metal-clad organic semiconductor microcavities” Adv. Opt. Mater. 1, 827-833 (2013)/Hutchison, J. A., Schwartz, T., Genet, C., Devaux, E. & Ebbesen, T. W. “Modifying chemical landscapes by coupling to the vacuum fields” Angew. Chem., Int. Ed. 51, 1592-1596 (2012)/Hutchison, J. A., Liscio, A., Schwartz, T., Canaguier-Durand, A., Genet, C., Palermo, V., Samori, P. & Ebbesen, T. W. “Tuning the work-function via strong coupling” Adv. Mater. 25, 2481-2485 (2013)/Canaguier-Durand, A., Devaux, E., George, J., Pang, Y., Hutchison, J. A., Schwartz, T. Genet, C., Wilhelms, N., Lehn, J.-M. & Ebbesen, T. W. “Thermodynamics of molecules strongly coupled to the vacuum field” Angew. Chem., Int. Ed. In press (2013)).
From WO 2013/017961 in particular, it is known to make use of strong coupling in order to modify the work function of materials (i.e. the energy required to extract an electron from the material) and the rate of chemical reactions.